We studied the electrophysiological change of the retina during ischemia-reperfusion in vivo cat. The electroretinogram (ERG), intraretinal ERG with microelectrodes and the change of ion concentration in the retina were recorded. In order to observe the change in potentials during reperfusion, retinal ischemia was induced by raising intraocular pressure. The ERG b- and c-wave after 10-30 minutes of ischemia were gradually recovered in 6 hours of reperfusion. After 30 minutes of ischemia complete recovery was not observed. To investigate the role of free radicals in reperfusion injury, superoxide dismutase and catalase, which were free radical scavengers, were given intravenously. Both agents did not show the significant improvement of ERG, although during early period the remarkable recovery of c-wave was observed. The intraretinal recordings showed similar recovery to the ERG.The photoreceptors and retinal pigment epithelium vere also damaged. The fact that the light-evoked alkalinizaton outside photoreceptors was reduced few hous after reperfusion suggests the reduction of photoreceptor's metabolism. The decrease of light-evoked [K+] change in that space suggests that the ion channel or pump function of photoreceptors is reduced.